A further cost for the sicker sex? Evidence for male-biased parasite-induced vulnerability to predation.

Jessica F Stephenson,Joanne Cable,Cock Van Oosterhout,Cormac Kinsella

doi:10.1002/ece3.2049

Abstract

Males are typically the sicker sex. Data from multiple taxa indicate that they are more likely to be infected with parasites, and are less “tolerant,” or less able to mitigate the fitness costs of a given infection, than females. One cost of infection for many animals is an increased probability of being captured by a predator. A clear, hitherto untested, prediction is therefore that this parasite‐induced vulnerability to predation is more pronounced among males than females. We tested this prediction in the sexually size dimorphic guppy, Poecilia reticulata, in which females are typically larger than males. We either sham or experimentally infected guppies with Gyrodactylus turnbulli, elicited their escape response using an established protocol and measured the distance they covered during 60 ms. To discriminate between the effects of body size and those of other inherent sex differences, we size‐matched fish across treatment groups. Infection with G. turnbulli reduced the distance covered during the escape response of small adults by 20.1%, whereas that of large fish was unaffected. This result implies that parasite‐induced vulnerability to predation is male‐biased in the wild: although there was no difference in escape response between our experimentally size‐matched groups of males and females, males are significantly smaller across natural guppy populations. These results are consistent with Bateman's principle for immunity: Natural selection for larger body sizes and longevity in females seems to have resulted in the evolution of increased infection tolerance. We discuss the potential implications of sex‐ and size‐biased parasite‐induced vulnerability to predation for the evolutionary ecology of this host–parasite interaction in natural communities.

Highlights

Male animals are widely considered the sicker sex: Typically they are more likely to be infected with parasites, and less able to mitigate the fitness costs of a given infection than females across taxa (Poulin 1996; Zuk and McKean 1996)
Guppies infected with Gyrodactylus turnbulli moved on average 9.9 mm less during the escape response than uninfected guppies, equating to a reduction of ~37% (Table 1)
Analysis using these categories indicated that small infected fish covered an average of 20.1% less distance in the first 60 ms of the escape response than small uninfected fish, but infection did not affect the distance covered by large fish (Fig. 3)

Summary

Introduction

Male animals are widely considered the sicker sex: Typically they are more likely to be infected with parasites, and less able to mitigate the fitness costs of a given infection (less “tolerant”; Raberg et al 2009) than females across taxa (Poulin 1996; Zuk and McKean 1996). A striking number of host–parasite interactions conform to this pattern (reviewed by Rolff 2002; SchmidHempel 2011). This difference is due to sexual selection driving divergent life-history strategies between the sexes (Bateman’s principle; Bateman 1948; Rolff 2002). Males maximize fitness by mating with as many females as possible; they invest more in male–male competition and reproduction, and generally have shorter life spans than females (Clutton-Brock and Isvaran 2007; Zuk 2009).

Methods

Results

Conclusion